Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art exhaust a complex mixture of air pollutants. These air pollutants can include, among other things, gaseous compounds such as the oxides of nitrogen (NOX). Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amount of NOX emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. In order to ensure compliance with the regulation of these compounds, some engine manufacturers have implemented a process called Selective Catalytic Reduction (SCR).
SCR is a process where a reductant (most commonly a urea/water solution) is injected into the exhaust gas stream of an engine and adsorbed onto a catalyst. The reductant reacts with NOX in the exhaust gas to form water (H2O) and elemental nitrogen (N2). Although SCR can be effective, when the reductant is sprayed onto relatively cool walls of the exhaust system it can condense. This condensation can create deposits that foul the injectors and cause premature wear and failure of the injection system. In addition, the condensed reductant may no longer be useful in reducing regulated emissions.
An exemplary dosing system is disclosed in U.S. Patent Publication No. 2013/0104531 of Cho et al. that published on May 2, 2013 (“the '531 publication”). Specifically, the '531 publication describes a system having an exhaust manifold, an SCR, and a static mixer connected between the exhaust manifold and the SCR. The static mixer includes an external tube, an internal tube, and a channel unit. The external tube is connected to the exhaust manifold by welding. The internal tube is disposed within the external tube and spaced apart therefrom by a constant gap. The channel unit is provided inside the internal tube, and includes multiple guiding channels in a longitudinal direction and an inlet portion facing a tilted urea injector adapter. The guiding channels have horizontal channel plates that are spaced apart at predetermined intervals and include through-holes that promote mixing. A plurality of blades are provided at an end point of the channel plates, and the blades are angled in opposing directions for each layer of plates. The inlet of the channel unit is inclined relative to an axis of the internal tube.
While the system of the '531 publication may reduce condensation through the use of the spaced apart walls and improve mixing via the through-holes and blades, the system may still be less than optimal. Specifically, because the system receives urea at a single location (i.e., at only the urea injector adapter), the injection of urea may be too concentrated or focused for efficient droplet dispersion within the exhaust stream. In addition, the geometry of the channel plates may be insufficient to adequately mix the injected urea with the exhaust.
The present disclosure is directed at overcoming one or more of the shortcomings set forth above and/or other problems of the prior art.